1. Field of the Invention
This invention relates to a vacuum processing apparatus for processing semiconductor wafers or other substrate samples in a decompressed processing chamber in a vacuum vessel while a processing gas is introduced into the processing chamber.
2. Description of the Related Art
Conventionally, in a vacuum processing apparatus for processing semiconductor wafers or other substrate samples to manufacture semiconductor devices, a processing chamber is placed in a vacuum vessel and decompressed to a predetermined degree of vacuum, and a processing gas is introduced into the processing chamber to form a desired feature on the semiconductor wafer surface. For example, an electric field is supplied from outside the vacuum vessel to a reactive gas introduced into the processing chamber to turn it into a plasma. By physical and chemical reactions with reactive particles such as ions and other charged particles and radicals in the plasma, a thin film previously formed on the wafer surface is processed into a desired feature.
The demand for higher integration of semiconductor devices requires such a vacuum processing apparatus to process a substrate surface with higher definition and accuracy. To meet such requirement, the sample surface must be processed more uniformly. For example, if the processing result significantly varies at different sites on the sample surface, a semiconductor device processed with a larger deviation from the desired feature fails to reach expected performance as compared with other devices, and the device manufacturing yield may decrease.
In view of this, for uniform processing, the processing gas introduced into the processing chamber is required to have a more uniform density distribution in the processing chamber. That is, it is known that such gas distribution greatly affects the uniformity of processing performance. Thus, conventionally, the introduction of gas is designed so that the gas distribution is uniform on the semiconductor wafer surface. For example, the processing chamber is shaped like a cylinder, the sample stage placed in the processing chamber for mounting a semiconductor wafer thereon has a generally cylindrical shape, and they are arranged coaxially or concentrically. Thus the processing performance is made uniform in the circumferential direction of a disc-shaped semiconductor wafer sample.
However, the temperature of a semiconductor wafer during processing and reaction products generated in processing the semiconductor wafer have radially nonuniform distribution. Recently, there is a demand for taking this into consideration to realize more uniform processing within the semiconductor wafer surface. For example, in a technique for enhancing the uniformity of processing performance, the component ratio of materials constituting a processing gas is varied radially with respect to the semiconductor wafer, and such a processing gas is supplied into the processing chamber above the semiconductor wafer so that each component has a different distribution above the semiconductor wafer.
An example conventional technique like this is disclosed in JP 62-290885A. In this conventional technique, cells are placed at the upside of the processing chamber and opposed to the semiconductor wafer. Processing gases of different species and flow rates are supplied to the electrode in the cells. A plurality of introduction holes for introducing the processing gases into the processing chamber are provided in communication with the cells, respectively. Gases of different gas species and gas flow rates are introduced from the gas introduction holes.
According to the configuration of such conventional technique, processing gases are introduced from a plurality of locations including the vicinity of the central axis and the vicinity of the outer periphery of the processing chamber into a space for plasma excitation and diffusion of the processing gases above the sample stage for mounting a wafer. Processing gases of different gas species and gas flow rates are introduced from these introduction locations to obtain a different concentration distribution for each gas species on the wafer surface.
In such conventional technique, in a processing chamber having a large space between the locations for introducing processing gases and the sample stage, the gas concentration distribution is flattened due to gas diffusion even if processing gases of different gas species and gas flow rates are introduced from different locations including the vicinity of the central axis and the vicinity of the outer periphery. Hence it is difficult to produce a biased distribution of gas concentration on the wafer surface. To overcome this difficulty, the variation of gas concentration distribution on the wafer surface can be increased by introducing processing gases from positions nearer to the wafer, e.g., from the side face of the processing chamber beside the above-mentioned space or from the surface on the outer periphery side of the sample stage (JP 10-064881A).
However, in the above conventional techniques, the following point is not sufficiently taken into consideration. In the conventional technique where gas is introduced from the vicinity of the wafer position to increase the variation of gas concentration distribution on the semiconductor wafer surface, introduction holes for introducing the processing gas must be provided on the inner surface of the processing chamber such as the side face of the processing chamber or the outer surface of the sample stage. Depending on the shape of the introducing hole, the distribution of the processing gas component in the processing chamber may be significantly deviated from the axisymmetrical distribution. Thus, unfortunately, the axisymmetrical plasma density in the processing chamber cannot be achieved, and the processing uniformity is significantly impaired.